Phenylbutazone, is one of the most popular and useful non-steroidal anti-inflammatory veterinary pharmaceuticals. It is typically the drug of choice for equine treatment when an illness or injury necessitates the use of a painkiller or anti-inflammatory medication. Phenylbutazone treats joint deterioration, swelling and inflammation from injuries, founder, fevers, and various other pains experienced by horses.
While phenylbutazone has been used to treat horses for more than thirty years, the administration of phenylbutazone persists in being the source of many problems. Phenylbutazone has a bitter taste, and is thus difficult to administer orally, but oral administration remains the desired mode of administration. The horses often reject the bitter drug, which leads to inconsistent dosages and difficulty in administering the drug.
Phenylbutazone is typically available to horse owners and veterinarians in one-gram tablets for oral administration. Horses do not willingly eat phenylbutazone tablets. Absent physical force, most horses will not swallow phenylbutazone tablets due to their bitterness. Thus, administration of these tablets involves first catching the horse and, depending on the individual personality and training of the horse, applying various degrees of restraints. Restraints range from a halter to prevent bobbing and weaving of the head, to more extreme measures that prevent rearing and kicking.
Horse owners and veterinarians have developed several means for the actual delivery of phenylbutazone to horses. In simple cases the tablets are crushed and mixed with the horse's food. This method is problematic because the crushed tablets do not adhere to the horse's food. Powder or granules sift to the bottom of the feeder as the horse eats. The amount of sifting varies with each administration and results in inconsistent dosages or diet problems due to the addition of feed to administer the remaining medication.
Some horses reject the grain and drug mixture altogether, requiring the additional step of mixing the crushed tablet with syrup or molasses before adding the bitter drug to the horse's feed. This method is problematic for several reasons. Syrup and molasses are very sticky, and the mixing process leaves a mess in the surrounding area as well as in the mixing container and feed trough or dish. This can result in a loss of medication and an inconsistent dose. In addition, the phenylbutazone is insoluble in syrup and molasses making it impossible to obtain a homogeneous mixture. If the mixture is not immediately administered to the horse, the phenylbutazone settles resulting in an inconsistent dosage or additional mixing requirements. Encapsulation of the crushed tablet matter by the syrup or molasses also hinders the speed at which digestive fluids can interact with the phenylbutazone and, consequently, blood absorption of phenylbutazone is delayed through the digestive process.
The various method of administering phenylbutazone to horses are unpleasant for the horse and the person, and can result in injury if the person administering the drug is bitten, pawed or stepped on by a stubborn horse. Because the medicine is bitter, a horse will continue to reject the medicine with increasing intensity over time. Ultimately, it becomes difficult or impossible to catch the horse three times a day for delivery of the drug and, if caught, the horse attempts to reject the medicine both before and after it is delivered.
The described administration problems with phenylbutazone would be merely inconvenient, except that they, in turn, cause serious problems, which are related to effective dosages. The drug is intended to control potentially chronic inflammation and pain, which can result in permanent soft tissue lesions, such as scarring of other fibroid tissue growth, as a consequence of long term chronic inflammation cycles. The drug provides relief from chronic cycles of inflammation and pain, and eventually facilitates increased range of motion without permanent loss of function. Thus, it is important to provide a method of administration that avoids peaks and valleys in the blood concentration levels of phenylbutazone arising from inconsistent dosage due to rejection or an inability to catch the horse for administration of the drug.
An important factor to consider in the delivery of phenylbutazone, in addition to methods for oral administration of the drug, is the speed at which the drug is absorbed into the horse's blood. Inflammation and pain are more easily relieved when effective treatment concentrations are attained more quickly. This is especially true when the inflammation is potentially associated with hemorrhaging due to soft tissue injury. Maintaining the proper blood concentration level, timing, and diet are critical to the effectiveness of the drug. Even so, it is commonly understood that mixing a drug with a carrier, such as a nutritional base for delivery of the drug, has the disadvantage of slowing down the blood absorption rate.
While a veterinarian should make the determination on an individual basis, a moderate dose for a 1000 pound horse is 1-2 grams or 5-10 cc per administration. Oral administration of phenylbutazone is slow to take effect, requiring 3-5 hours to achieve an effective concentration level. Three dosages per day should be administered to maintain the proper blood concentration level. However, due to the problems with oral administration, most horse owners and veterinarians settle for a double or sometimes only a single dosage per day, as opposed to the ideal triple dosage. Administration and dosage problems are compounded where prolonged treatments are required for treatment of chronic soft tissue injuries, and these problems can result in significant health effects to the horse and cost burden on the owner.
Some efforts have been made to improve the delivery of phenylbutazone to horses. U.S. Pat. No. 6,022,563 describes carrier formulations which ease administration of the medicine to the horse. While the formulations provided improved the ability to induce the horse to eat the medicine, there remained some difficulty in administering the medicine to the horse. Additionally, the carrier formulations provided showed little increase in the horse phenylbutazone blood concentration as compared to pure phenylbutazone tablets. Because of the difficulty in administering phenylbutazone and the rejection of the same by horses discussed above, it would be desirable to have a more easily administered formulation and to achieve increased blood concentrations in horses.
Therefore, there is a need for an improved carrier formulation of phenylbutazone that is more palatable to horses than prior formulations, that is easily administered in a proper dosage without special skills or alteration from its manufactured state, and provides quicker absorption into the bloodstream and increased blood concentrations.